Experimental study on yield behavior of Daqing crude oil

The yield behavior of Daqing crude oil was studied by means of multi-mode controlled-stress tests with a high-precision stress controlled rheometer. Two experiments of creep and constant stress loading rate were performed. The yield stress of gelled crude oil was dependent on the test conditions such as the stress loading time and the stress loading rate, but the yield strain did not change with test conditions. The yield strain did exist objectively and it can be used as the criterion for the yielding of the structure of gelled crude oil. The yield strain of gelled oil was studied through experiments of creep, constant stress loading rate, oscillatory shear stress increase, and constant shear rate. The yield strain of gelled crude oil decreased with the increasing gel strength. The experiment of constant speed increase of stress showed the strain softening phenomena for low gel strength oil.